1. Field of the Invention
The present invention relates to a process and a system for extracting sulfur from a gas stream. More particularly, the present invention relates to a process and a system for desulfurizing a gas stream using a plurality of solid adsorbent beds.
2. Description of Prior Art
Refinery streams are typically desulfurized by the Claus process wherein elemental sulfur is produced by reacting hydrogen sulfide and sulfur dioxide in the presence of a catalyst. The Claus system uses a combustion chamber which, at 1800.degree. F. to 2800.degree. F., converts 50 to 70% of sulfur contained in the feed gas into elemental sulfur. Sulfur is condensed by cooling the reaction gas to a temperature below the dew point of sulfur after which the remaining gas is heated and further reacted over a catalyst. Normally, the gas passes through at least two such Claus catalyst stages.
The different stages of the process may be represented by the following equations: EQU H.sub.2 S+3/2O.sub.2 .fwdarw.SO.sub.2 +H.sub.2 O EQU 2H.sub.2 S+SO.sub.2 .fwdarw.3S+2H.sub.2 O
The overall reaction is: EQU 3H.sub.2 S+3O.sub.2 .fwdarw.3S+3H.sub.2 O
The final Claus exhaust gas still contains small amounts of H.sub.2 S, SO.sub.2, CS.sub.2, carbon oxysulfide, CO, and elemental sulfur in the form of a vapor or mist. The exhaust gas can be subjected to post-combustion to convert substantially everything to SO.sub.2 and then further purified by Claus after-treatments.
An after-treatment process which oxidizes all sulfur compounds into SO.sub.2 is disclosed in U.S. Pat. No. 3,764,665 which disclosed a process for removing sulfur oxides from gas mixtures with a solid acceptor for sulfur oxides wherein the solid acceptor is regenerated with a steam-diluted reducing gas and the regeneration off-gas is fed to a Claus sulfur recovery process. The regeneration off-gas is cooled to condense the water vapor contained therein, the cooled off-gas is contacted with a sulfur dioxide-selective liquid absorbent, and the liquid absorbent is passed to a buffer zone and then to a stripping zone wherein the absorbed SO.sub.2 is recovered from the liquid absorbent and is supplied to the sulfur recovery process. By operating in this manner, fluctuations in the sulfur dioxide concentration of the regeneration off-gas are leveled-out and a relatively concentrated sulfur dioxide stream is supplied to the sulfur recovery process at a relatively constant rate.
Although the process of U.S. Pat. No. 3,764,665 supplies relatively concentrated sulfur dioxide to the sulfur recovery process at a substantially constant rate, the off-gas must be cooled and the liquid absorbent must be transferred to a buffer zone before the absorbed SO.sub.2 can be stripped. Therefore, what is needed is a simpler process whereby these steps are eliminated and energy costs reduced.